1984 R100RT.... What to look for.

[viejo]

I'm going to be looking at a fairly low mileage '84 R100RT (LE) shortly and I'm wondering if there is anything in particular I should be looking for. I've had several Airheads in the past, still have two, but early '70s /5 is as recent as I've had hands on experience with so I thought I'd get some "adult supervision".

Mil Gracias,

Dave

 

[20774]

Dave -

You probably have a good idea of what sort of wear-points you want to look for as well as general cosmetics if that concerns you. What does "fairly low mileage" translate to? For the '81-84 bikes, the issue was that BMW used the wrong valve seat material that didn't transfer heat very well into the heads. When the valve face settles on the seat for that fraction of a second, heat is supposed to be pulled off the valve. But with the wrong material, the heat didn't necessarily transfer. The result was that the valves retained heat and the valve face could begin to warp or tulip. Heat is the issue and an RT and 1000cc engine tends to add even more heat. So, I'd wonder if the current owner has had any issues with valve clearances remaining stable. In time, the bike likely will need a top end rebuild using newer valve and seat material.

The 1984 is on the cusp of another thing BMW did in the transmission. They eliminated a circlip to save a buck and the result can be that the shafts in the box can migrate some. The time periods is generally 1985-1995 -ish but there is some variance due to when the bikes were coming through the assembly line. Snowbum has discussed this on his site. Anton has a good overview of this issue as well.

Circlip failure

Circlip problem with Airhead transmission

largiader.com

Neither of these issues are catastrophic...they just require rebuilds when/if the problems show up.

 

[viejo]

Kurt,

Thanks for the good input!

First- The instrument cluster picture furnished by the current owner shows ~42k on the clock. I will be checking a number of other indicators to confirm this one way or another. With the advent of the Nikasil cylinders I consider this to be low to moderate.

Second- I am aware of the deficient metallurgy in the early '80s cylinder heads and will probably have the heads refurbished before putting any serious miles on the bike (assuming this has not already been done).... possibly/probably even double plugging.

I was very pleased to see your references to both Snowbum and Anton. The MOA forums are a good cut above average when it comes to the competence/reliability of some of the posters, but I consider both of those guys to be among the best of the best. I will dig a little deeper to see if I can pinpoint exactly when BMW began omitting the transmission circlip. (That used to be one of Oaks favorite rants on the Airheads Beemer Club tech forum....that and the $3k oil filter o-ring. I miss him.)

Dave

 

[stevenrankin]

The RT will have the in my mind dang rear disc brake system. In my experience, this is prone to very fast wear of pads and rotor compared to the brakes on the front end. Anything over 35K miles, I would inspect the pads.
Other than the issues with the valves Kurt mentions, the 84 RT was and is a very good bike. Albeit not as powerful as the pre 82 R100RT bikes due to increased EPA restrictions. Good luck and buying, St.

 

[ksdcr]

Dave,

I resurrected a 1983 R100T a few years ago, with similar mileage. Mine had been used infrequently, and needed some rehab, including a complete tear down of both carbs, ultrasonic cleaned and all new components. Along with balancing the Bings, I checked valve clearance.. Additionally, lots of rubber parts were unserviceable, so needed replacement. I proactively changed a few cables, including the speedometer and clutch cables. Also, every fluid, oil, transmission, brakes, driveshaft etc.were renewed. New glas mat battery, that is now over 4 years. The tires on mine were in good condition with almost new tread, but, had been mounted 10 years before. So, new tire and tubes for peace of mind. I also found that the seat pan had weakened at the hinge locations, with spider cracks. I was fortunate to locate a NOS seat online, with a perfect pan, cover and foam. After recommissioning the R100,

I’ve put over 10,000 trouble free miles in the past four years. Good luck with your RT, it’s not just a nice touring bike, it’s a classic airhead.

John

 

[viejo]

I went to view the bike yesterday and the first things I noticed were a kickstart transmission, rear drum brake, and pursuit light fairing nacelles..... turns out "LE" meant Law Enforcement and not Last Edition (as hoped). The bike also had a "heel and toe" shifter that looked to be straight out of Tractor Supply; something about the LEO's boots not being compatible with the stock shift lever. I did inspect and test ride the bike and found it to be a good one (although desperately in need of new SS brake lines) but, unfortunately, just a few too many "LE" mods to overcome. The pursuit light assemblies replaced the air ducts found on the standard RT fairing, and in the Texas summer you need all the ventilation you can get.

The hunt continues...... thanks for all the good input!

Dave

 

[ksdcr]

That is a shame. These old airheads can be a lot of fun. Commuting, sport touring or anything in between, as they are very capable bikes.

 

[viejo]

I'm now on the trail of an '82 R100RS and a '78 R100RS. I put about 150k on a '76 R90/6 years ago so I'm pretty keen to get a look at the '78. The chase is on.....